Optical compensation film and retardation film

ABSTRACT

To provide a retardation film and an optical compensation film which have excellent optical properties and are useful as a compensation film for compensating the contrast and viewing-angle characteristics of liquid-crystal displays and as an antireflection film.

FIELD OF THE INVENTION

The present invention relates to an optical compensation film and aretardation film which have excellent optical properties, such as a highrefractive index in the film thickness direction, a large in-planeretardation, and a small wavelength dependence, and are effective inimproving the contrast and viewing-angle characteristics ofliquid-crystal displays.

BACKGROUND ART

Liquid-crystal displays are in extensive use as most important displaydevices in multimedia societies in applications ranging from cell phonesto computer monitors, notebook type personal computers, and TVs. Manyoptical films are used in a liquid-crystal display for improving displaycharacteristics. In particular, retardation films play major roles suchas an improvement in contrast for viewing from the front and obliquedirections and color tone compensation. Although retardation films madeof polycarbonates and polycycloolefins have been used hitherto, thesepolymers each are a polymer having positive birefringence. Thepositiveness or negativeness of birefringence is defined in thefollowing manner.

The optical anisotropy of a polymer film which has undergone molecularorientation by, e.g., stretching can be expressed with the indexellipsoid shown in FIG. 1. In the film which has been stretched, therefractive index in a fast-axis direction of the film plane, therefractive index in an in-plane direction perpendicular to the fast-axisdirection, and the refractive index in an out-of-plane verticaldirection are expressed by nx, ny, and nz, respectively. Incidentally,the fast-axis is an in-plane axial direction in which the refractiveindex is low.

Negative birefringence means the case where the stretching directionbecomes the fast-axis direction, while positive birefringence means thecase where a direction perpendicular to the stretching direction becomesthe fast-axis direction.

Namely, the uniaxial stretching of a polymer having negativebirefringence results in a reduced refractive index in the stretchingaxis direction (fast-axis: stretching direction), while the uniaxialstretching of a polymer having positive birefringence results in areduced refractive index in an axial direction perpendicular to thestretching axis direction (fast-axis: direction perpendicular tostretching direction).

Furthermore, in-plane retardation (Re) is expressed as a value obtainedby multiplying the value of [refractive index in an in-plane directionperpendicular to the fast-axis direction (ny)]−[refractive index in afast-axis direction of the film plane (nx)] by the film thickness.

Many polymers have positive birefringence. Polymers having negativebirefringence include acrylic resins and polystyrene. However, acrylicresins are low in the ability to develop retardation, and showinsufficient properties when used as an optical compensation film.Polystyrene has: a problem concerning retardation stability that it hasa large modulus of photoelasticity in a room temperature region andchanges in retardation with a slight stress; a problem concerningoptical properties that it has a large wavelength dependence ofretardation; and a problem concerning practical use that it has low heatresistance. Presently, polystyrene is not in use.

The term wavelength dependence of retardation means that a retardationchanges with measuring wavelength. It can be expressed as the ratio ofthe retardation as measured at a wavelength of 450 nm (R450) to theretardation as measured at a wavelength of 550 nm (R550), i.e.,R450/R550. In general, polymers having an aromatic structure highly tendto have a large value of R450/R550, and use of such polymers results ina decrease in contrast in a short-wavelength region and a decrease inviewing angle characteristics.

A stretched film of a polymer showing negative birefringence has ahigher refractive index in the film thickness direction and can be anovel optical compensation film. It is hence useful as an opticalcompensation film for compensating the viewing angle characteristics ofdisplays such as a super twisted nematic liquid-crystal display(STN-LCD), vertical-alignment liquid-crystal display (VA-LCD), in-planeswitching liquid-crystal display (IPS-LCD), reflection typeliquid-crystal display, and semi-transmissive liquid-crystal display oras an optical compensation film for compensating the viewing-anglecharacteristics of polarizers. There is a strong desire on the marketfor an optical compensation film having negative birefringence. Using apolymer having positive birefringence, processes for producing a filmhave been proposed to produce a film having a heightened refractiveindex in the thickness direction. One of these is a method of treatmentwhich comprises bonding a heat-shrinkable film to one or each side of apolymer film and stretching the laminate with heating to apply ashrinkage force in the thickness direction for the polymer film (see,for example, patent documents 1 to 3). Also proposed is a method inwhich a polymer film is uniaxially stretched in an in-plane directionwhile applying an electric field thereto (see, for example, patentdocument 4). Furthermore, a retardation film comprising fine particleshaving negative optical anisotropy and a transparent polymer has beenproposed (see, for example, patent document 5). An optical compensationfilm or optical compensation layer obtained by applying aliquid-crystalline polymer film and causing the polymer to undergohomeotropic orientation has been proposed (see, for example, patentdocument 6). An optical compensation film having a coating of anaromatic polymer such as polyvinylnaphthalene or polyvinylbiphenyl hasalso been proposed (see, for example, patent document 7 and non-patentdocument 1).

Moreover, an optical film comprising a polyvinylcarbazole type polymerhas been proposed (see, for example, patent document 8).

A plastic substrate, optical film, and retardation film for displayshave been proposed which comprise a fumaric diester resin or acrosslinked fumaric diester resin (see, for example, patent documents 9and 10).

[Patent Document 1] Japanese Patent No. 2818983

[Patent Document 2] JP-A-05-297223

[Patent Document 3] JP-A-05-323120

[Patent Document 4] JP-A-06-088909

[Patent Document 5] JP-A-2005-156862

[Patent Document 6] JP-A-2002-333524

[Patent Document 7] JP-A-2006-221116

[Patent Document 8] JP-A-2001-91746

[Patent Document 9] JP-A-2005-97544

[Patent Document 10] JP-A-2006-249318

[Non-Patent Document 1] The Society of Rheology, Japan, vol. 22, No. 2pp. 129-134 (1994)

SUMMARY OF THE INVENTION

However, the methods proposed in patent documents 1 to 4 have a problemthat the production steps are highly complicated, resulting in poorproductivity. Furthermore, control for attaining, e.g., retardationevenness is exceedingly difficult as compared with conventional controlby stretching. In the case where a polycarbonate is used as a base film,the film produced has a large photoelasticity constant at roomtemperature and has a problem concerning retardation stability that itchanges in retardation with a slight stress. This film has otherproblems, for example, that it has a large wavelength dependence ofretardation.

The optical retardation film obtained according to patent document 5 isan optical retardation film having negative birefringence impartedthereto by adding fine particles having negative optical anisotropy.However, from the standpoints of production process simplification andprofitability, there is a desire for an optical retardation film forwhich the addition of fine particles is unnecessary. The methoddescribed in patent document 6 has a problem that it is difficult tocause a liquid-crystalline polymer to evenly undergo homeotropicorientation. The techniques described in patent documents 7 and 8 haveproblems that the film obtained is apt to crack and has highwavelength-dispersability of the retardation.

Although patent document 9 proposes a plastic substrate for displayswhich comprises a fumaric diester resin, no proposal is made therein onan optical compensation film or retardation film.

In patent document 10, a retardation film is obtained by crosslinkingand stretching a fumaric diester resin. This film, however, has a smallretardation and has had a problem concerning practical use as aretardation film.

Accordingly, an object of the invention is to provide an opticalcompensation film or optical compensation layer and a retardation filmwhich are excellent in optical properties and mechanical properties.

The present inventors made intensive investigations in view of theproblems described above. As a result, they have found that the problemsdescribed above are eliminated with an optical compensation film and aretardation film which comprise a film or layer of a specific resin andin which the three-dimensional refractive indexes of the film or layersatisfy a specific relationship. The invention has been thus completed.

The invention relates to: an optical compensation film or opticalcompensation layer which is a film or layer comprising a fumaric esterresin, the film or layer having three-dimensional refractive indexessatisfying the relationship nz>ny≧nx, wherein nx is the refractive indexin a fast-axis direction of the film plane or layer plane, ny is therefractive index in an in-plane direction perpendicular to the fast-axisdirection, and nz is the refractive index in an out-of-plane verticaldirection (referred to also as the refractive index in the filmthickness direction), the ratio of the retardation as measured at awavelength of 450 nm to the retardation as measured at a wavelength of550 nm (R450/R550) being 1.1 or lower (film (A)); an opticalcompensation film which comprises the film (A) and a film (B) which hasthree-dimensional refractive indexes satisfying the relationshipny>nx≧nz, wherein nx is the refractive index in a fast-axis direction ofthe film plane, ny is the refractive index in an in-plane directionperpendicular to the fast-axis direction, and nz is the refractive indexin an out-of-plane vertical direction, and which has an in-planeretardation (Re) as measured at a wavelength of 550 nm of 50 nm orlarger; a retardation film which is a film comprising a fumaric esterresin and in which when the refractive index in a fast-axis direction ofthe film plane, the refractive index in an in-plane directionperpendicular to the fast-axis direction, and the refractive index in anout-of-plane vertical direction are expressed by nx, ny, and nz,respectively, the refractive indexes satisfy the relationship nx<ny≦nz;and a retardation film comprising a film (C) which is a film comprisinga fumaric ester resin and in which when the refractive index in afast-axis direction of the film plane, the refractive index in anin-plane direction perpendicular to the fast-axis direction, and therefractive index in an out-of-plane vertical direction are expressed bynx, ny, and nz, respectively, the refractive indexes satisfy therelationship nx<ny≦nz and a film (D) which has three-dimensionalrefractive indexes satisfying the relationship ny>nx≧nz or ny>nz≧nx,wherein nx is the refractive index in a fast-axis direction of the filmplane, ny is the refractive index in an in-plane direction perpendicularto the fast-axis direction, and nz is the refractive index in anout-of-plane vertical direction.

The invention can provide an optical compensation film and a retardationfilm which have excellent optical properties and are useful as acompensation film for improving the contrast and viewing-anglecharacteristics of liquid-crystal displays and as an antireflectionfilm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows changes of a refractive index ellipsoid with stretching.

Numerical References and Signs in Figs. are described.

nx: refractive index in a fast-axis direction of the film plane.

ny: refractive index in an in-plane direction perpendicular to nx.

nz: refractive index in an out-of-plane vertical direction.

DETAILED DESCRIPTION OF THE INVENTION

The optical compensation film and retardation film of the invention willbe explained below in detail.

The optical compensation film of the invention is explained first.

The optical compensation film of the invention is an opticalcompensation film or optical compensation layer which is a film or layercomprising a fumaric ester resin, the film or layer havingthree-dimensional refractive indexes satisfying the relationshipnz>ny≧nx, especially preferably the relationship nz>ny≈nx, wherein nx isthe refractive index in a fast-axis direction of the film plane or layerplane, ny is the refractive index in an in-plane direction perpendicularto the fast-axis direction, and nz is the refractive index in anout-of-plane vertical direction, the ratio of the retardation asmeasured at a wavelength of 450 nm to the retardation as measured at awavelength of 550 nm (R450/R550) being 1.1 or lower. The refractiveindex nx in a fast-axis direction of the film plane or layer plane meansthe refractive index as measured in the direction which is the lowest inrefractive index in the film plane or layer plane. The values of nx, ny,and nz can be determined, for example, with a sample inclination typeautomatic birefringence analyzer.

Although the optical compensation film of the invention is an opticalcompensation film or layer comprising a fumaric ester resin, this layercomprising a fumaric ester resin means a fumaric ester resin part formedby bonding the fumaric ester resin to, e.g., a substrate.

In general, the three-dimensional refractive indexes of a film areregulated by film stretching or the like and this results in complicatedproduction steps and complicated quality control. In contrast, filmsmade of a fumaric ester resin exhibit such a peculiar behavior that thefilm in an unstretched state has a higher refractive index in the filmthickness direction.

The optical compensation film or optical compensation layer of theinvention preferably is one in which the out-of-plane retardation (Rth)represented by the following expression (1), wherein d is the thicknessof the film, is from −30 to −2,000 μm. The out-of-plane retardationthereof is especially preferably from −50 to −1,000 nm, even morepreferably from −100 to −500 nm.Rth=[(nx+ny)/2−nz]×d  (1)

The wavelength dependence of retardation can be expressed by the ratioof the retardation as measured at a wavelength of 450 nm (R450) to theretardation as measured at a wavelength of 550 nm (R550), i.e., theratio R450/R550. In the optical compensation film or opticalcompensation layer of the invention, the value of R450/R550 is 1.1 orlower. In particular, that ratio is preferably 1.08 or lower, morepreferably 1.05 or lower.

Examples of the fumaric ester resin to be used in the invention includepolymers of fumaric esters. Preferred of these is a fumaric ester resincomprising at least 50% by mole fumaric diester residue unitsrepresented by formula (a). In particular, a resin in which theproportion of the fumaric diester residue units is 70% by mole or higheris more preferred because it gives an optical compensation film oroptical compensation layer excellent in heat resistance and mechanicalproperties. In especially, the proportion of these units is 80% by moleor higher, and even more preferably, the proportion of these units is90% by mole or higher.

(In the formula, R₁, and R₂ each independently represent a branchedalkyl or cyclic alkyl group having 3-12 carbon atoms.)

Ester substituents R₁ and R₂, which independently are a branched alkylor cyclic alkyl group having 3-12 carbon atoms, in the fumaric diesterresidue units may have been substituted with a halogen, e.g., fluorineor chlorine, or an ether, ester, or amino group. Examples of R₁ and R₂include isopropyl, s-butyl, t-butyl, s-pentyl, t-pentyl, s-hexyl,t-hexyl, cyclopropyl, cyclopentyl, and cyclohexyl. R₁ and R₂ especiallypreferably are isopropyl, s-butyl, t-butyl, cyclopentyl, cyclohexyl, orthe like because such fumaric diester residue units enable the resin togive an optical compensation film or optical compensation layerexcellent in heat resistance and mechanical properties. Isopropyl ismore preferred of these because it enables the resin to give an opticalcompensation film or optical compensation layer having an excellentbalance between heat resistance and mechanical properties.

Examples of the fumaric diester residue units represented by formula (a)include a diisopropyl fumarate residue, di-s-butyl fumarate residue,di-t-butyl fumarate residue, di-s-pentyl fumarate residue, di-t-pentylfumarate residue, di-s-hexyl fumarate residue, di-t-hexyl fumarateresidue, dicyclopropyl fumarate residue, dicyclopentyl fumarate residue,and dicyclohexyl fumarate residue. Preferred of these are a diisopropylfumarate residue, di-s-butyl fumarate residue, di-t-butyl fumarateresidue, dicyclopentyl fumarate residue, and dicyclohexyl fumarateresidue. Especially preferred is a diisopropyl fumarate residue.

The fumaric ester resin comprising at least 50% by mole fumaric diesterresidue units represented by formula (a), which is a preferred resin foruse as the fumaric ester resin in the invention, is a resin made up ofat least 50% by mole fumaric diester residue units represented byformula (a) and up to 50% by mole residue units derived from one or moremonomers copolymerizable with fumaric diesters. Examples of the residueunits derived from one or more monomers copolymerizable with fumaricdiesters include one or more kinds selected from styrene compoundresidues such as a styrene residue and an α-methylstyrene residue; anacrylic acid residue; acrylic ester residues such as a methyl acrylateresidue, ethyl acrylate residue, butyl acrylate residue,3-ethyl-3-oxetanylmethyl acrylate residue, and tetrahydrofurfurylacrylate residue; a methacrylic acid residue; methacrylic ester residuessuch as a methyl methacrylate residue, ethyl methacrylate residue, butylmethacrylate residue, 3-ethyl-3-oxetanylmethyl methacrylate residue, andtetrahydrofurfuryl methacrylate residue; vinyl ester residues such as avinyl acetate residue and a vinyl propionate residue; an acrylonitrileresidue; a methacrylonitrile residue; and olefin residues such as anethylene residue and a propylene residue. Preferred of these are a3-ethyl-3-oxetanylmethyl acrylate residue and a 3-ethyl-3-oxetanylmethylmethacrylate residue. Especially preferred is a 3-ethyl-3-oxetanylmethylacrylate residue.

The fumaric ester resin to be used in the invention preferably is onewhich has a number-average molecular weight (Mn), as determined from anelution curve obtained by gel permeation chromatography (hereinafterreferred to as GPC) through calculation for standard polystyrene, of1×10³ or higher. In particular, the number-average molecular weightthereof is preferably from 2×10⁴ to 2×10⁵ because this resin gives anoptical compensation film or optical compensation layer excellent inmechanical properties and in moldability in film formation.

For producing the fumaric ester resin to be used for constituting theoptical compensation film or optical compensation layer of theinvention, any process may be used as long as the fumaric ester resin isobtained. For example, the resin can be produced by subjecting a fumaricdiester optionally together with one or more monomers copolymerizablewith the fumaric diester to radical polymerization or radicalcopolymerization. Examples of this fumaric diester include diisopropylfumarate, di-s-butyl fumarate, di-t-butyl fumarate, di-s-pentylfumarate, di-t-pentyl fumarate, di-s-hexyl fumarate, di-t-hexylfumarate, dicyclopropyl fumarate, dicyclopentyl fumarate, anddicyclohexyl fumarate. Examples of the monomers copolymerizable with thefumaric diester include one or more kinds selected from styrenecompounds such as styrene and α-methylstyrene; acrylic acid; acrylicesters such as methyl acrylate, ethyl acrylate, butyl acrylate,3-ethyl-3-oxetanylmethyl acrylate, and tetrahydrofurfuryl acrylate;methacrylic acid; methacrylic esters such as methyl methacrylate, ethylmethacrylate, butyl methacrylate, 3-ethyl-3-oxetanylmethylmethacrylate,and tetrahydrofurfuryl methacrylate; vinyl esters such as vinyl acetateand vinyl propionate; acrylonitrile; methacrylonitrile; and olefins suchas ethylene and propylene. Preferred of these are3-ethyl-3-oxetanylmethyl acrylate and 3-ethyl-3-oxetanylmethylmethacrylate. Especially preferred is 3-ethyl-3-oxetanylmethyl acrylate.

The radical polymerization can be conducted by known polymerizationmethods. For example, any of the bulk polymerization method, solutionpolymerization method, suspension polymerization method, precipitationpolymerization method, emulsion polymerization method, and the like canbe employed.

Examples of polymerization initiators usable in the radicalpolymerization include organic peroxides such as benzoyl peroxide,lauryl peroxide, octanoyl peroxide, acetyl peroxide, di-t-butylperoxide, t-butyl cumyl peroxide, dicumyl peroxide, t-butylperoxyacetate, t-butyl peroxybenzoate, and t-butyl peroxypivalate; andazo initiators such as 2,2′-azobis(2,4-dimethylvaleronitrile),2,2′-azobis(2-butyronitrile), 2,2′-azobisisobutyronitrile, dimethyl2,2′-azobisisobutyrate, and 1,1′-azobis(cyclohexane-1-carbonitrile).

Solvents usable in the solution polymerization method, suspensionpolymerization method, precipitation polymerization method, and emulsionpolymerization are not particularly limited. Examples thereof includearomatic solvents such as benzene, toluene, and xylene; alcohol solventssuch as methanol, ethanol, propyl alcohol, and butyl alcohol;cyclohexane; dioxane; tetrahydrofuran (THF); acetone; methyl ethylketone; dimethyl formamide; isopropyl acetate; and water. Examplesthereof further include mixtures of two or more of these.

The polymerization temperature to be used for the radical polymerizationcan be suitably determined according to the decomposition temperature ofthe polymerization initiator. In general, it is preferred to conduct thepolymerization at a temperature in the range of 40-150° C.

The optical compensation film of the invention may be an opticalcompensation film (film (E)) which comprises the optical compensationfilm or optical compensation layer of the invention (film (A)) and afilm (B) which has three-dimensional refractive indexes satisfying therelationship ny>nx≧nz, wherein nx is the refractive index in a fast-axisdirection of the film plane, ny is the refractive index in an in-planedirection perpendicular to the fast-axis direction, and nz is therefractive index in an out-of-plane vertical direction and which has anin-plane retardation (Re) as measured at a wavelength of 550 nm andrepresented by the following expression (2), wherein d is the thicknessof the film, of 50 nm or larger.Re=(ny−nx)×d  (2)

Film (B), which is a film having three-dimensional refractive indexessatisfying the relationship ny>nx≧nz, can be obtained, for example, byuniaxially stretching a polymer having positive birefringence.

The polymer constituting film (B) is not particularly limited as long asit is a polymer having positive birefringence. From the standpoints ofheat resistance, transparency, etc., preferred examples of such polymersinclude polycarbonate resins, polyethersulfone resins, polycycloolefinresins, and N-substituted maleimide resins. The in-plane retardation(Re) of film (B) is preferably 50 nm or larger, especially preferably100 nm or larger, even more preferably 120 nm or larger.

In film (E), the orientation parameter (Nz) represented by the followingexpression (3) is preferably from −0.1 to 0.95, provided that nx is therefractive index in a fast-axis direction of the film plane, ny is therefractive index in an in-plane direction perpendicular to the fast-axisdirection, nz is the refractive index in an out-of-plane verticaldirection, and d is the thickness of the film. For viewing anglecompensation especially in STN-LCDs, IPS-LCDs, reflection type LCDs, andsemi-transmissive LCDs, the Nz of film (E) is preferably 0.40-0.60, morepreferably 0.45-0.55. For viewing angle compensation in polarizers, theNz thereof is preferably from −0.10 to 0.10, especially preferably from−0.05 to 0.05, even more preferably 0-0.05.Nz=(ny−nz)/(ny−nx)  (3)

Furthermore, in film (E), the in-plane retardation (Re) represented byexpression (2) is preferably 50-1,000 nm, especially preferably 100-500nm. When film (E) is for use as a quarter-wave plate or a half-waveplate, the in-plane retardation thereof is preferably 130-140 nm or270-280 nm, respectively.

Processes for producing the optical compensation film comprising afumaric ester resin, among the optical compensation films according tothe invention, are not particularly limited. For example, it can beproduced by the solution casting method, melt casting method, or thelike.

The solution casting method is a method comprising casting a solutionprepared by dissolving a fumaric ester resin in a solvent (hereinafterthe solution is referred to as dope) on a supporting base and thenremoving the solvent by heating, etc. to obtain a film. For casting thedope on a supporting base in this method, use may be made of a techniquesuch as, e.g., the T-die method, doctor blade method, bar coater method,roll coater method, lip coater method, or the like. In particular, themethod in most common industrial use is to continuously extrude the dopethrough a die onto a supporting base in a belt or drum shape. Examplesof the supporting base to be used include glass substrates; metalsubstrates such as stainless-steel substrates and ferrotype substrates;and plastic substrates made of poly(ethylene terephthalate) (PET) andcellulosic resins such as triacetylcellulose (TAC). The thus-obtainedfilm made of a fumaric ester resin may be peeled from the supportingbase before use. Alternatively, in the case where the supporting baseused is a glass substrate or a plastic substrate, the film can be usedin the form of this laminate without being peeled from the substrate. Inorder for the solution casting method to form a film having hightransparency and excellent in thickness precision and surfacesmoothness, the solution viscosity of the dope is an exceedinglyimportant factor. The viscosity thereof is preferably 700-30,000 cps,especially preferably 1,000-10,000 cps. On the other hand, the meltcasting method is a molding method which comprises melting a fumaricester resin in an extruder, extruding the melt in a film form throughthe slit of a T-die, and then hauling the extrudate while cooling itwith a roll, air, etc.

Processes for producing the optical compensation film comprising theoptical compensation film or optical compensation layer (film (A)) andfilm (B) are not particularly limited and film (A) is a preferredoptical compensation film or optical compensation layer according to theinvention. For example, it can be produced by a method in which anunstretched film made of a fumaric ester resin is laminated to a filmobtained by uniaxially stretching a film having positive birefringence(hereinafter referred to as process 1) or a method in which a fumaricester resin is applied to a film obtained by uniaxially stretching afilm having positive birefringence (hereinafter referred to as process2).

Examples of the film having positive birefringence in processes 1 and 2include films made of polycarbonate resins, polyethersulfone resins,polycycloolefin resins, N-substituted maleimide resins, or the like.This film having positive birefringence is uniaxially stretched, forexample, under the conditions of a temperature of 150-200° C.,stretching speed of 10-30 mm/min, and stretch ratio of 30-70%, whereby auniaxially stretched film can be produced from the film having positivebirefringence.

In process 1, a film obtained by uniaxially stretching a film havingpositive birefringence is laminated to an unstretched film made of afumaric ester resin, whereby the optical compensation film can beproduced. In this laminating, a roll-to-roll continuous process, forexample, can be used to produce the optical compensation film. For thislaminating, a known adhesive can be used.

In process 2, a fumaric ester resin is applied to a film obtained byuniaxially stretching a film having positive birefringence, whereby theoptical compensation film can be produced. As a result, an opticalcompensation film composed of the film obtained by uniaxially stretchinga film having positive birefringence and a layer made of the fumaricester resin is produced. For the application, use may be made of amethod which comprises applying a solution (coating solution) preparedby dissolving a fumaric ester resin in a solvent to the film andremoving the solvent by heating, etc. For the application, use may bemade of a technique such as, e.g., the doctor blade method, bar coatermethod, gravure coater method, slot die coater method, lip coatermethod, comma coater method, or the like. Techniques in generalindustrial use are the gravure coater method for thin-film applicationand the comma coater method for thick-film application. In order for thesolution application to form a coating having high transparency andexcellent in thickness precision and surface smoothness, the viscosityof the coating solution is an exceedingly important factor. Theviscosity thereof is preferably 10-10,000 cps, especially preferably10-5,000 cps. The application thickness of the fumaric ester resin foruse in the invention (thickness of the layer made of the fumaric esterresin) is determined according to the retardation in the film thicknessdirection. The thickness thereof on a dry basis is preferably 1-200 μm,especially preferably 10-100 μm. It is possible to subject a surface ofthe film (B) to an adhesion-facilitating treatment beforehand.

The optical compensation film of the invention may be laminated toitself or to another optical compensation film.

It is preferred that an antioxidant should have been incorporated in theoptical compensation film of the invention in order to enhance thethermal stability thereof. Examples of the antioxidant includehindered-phenol antioxidants, phosphorus compound antioxidants, andother antioxidants. These antioxidants may be used alone or incombination of two or more thereof. It is preferred to use a combinationof a hindered-phenol antioxidant and a phosphorus compound antioxidantbecause it performs a synergistically improved antioxidant function. Inthis case, it is especially preferred to mix and use the twoingredients, for example, in such a proportion that the amount of thephosphorus compound antioxidant is 100-500 parts by weight per 100 partsby weight of the hindered-phenol antioxidant. The amount of theantioxidants to be added is preferably 0.01-10 parts by weight,especially preferably 0.5-1 part by weight, per 100 parts by weight ofthe fumaric ester resin constituting the optical compensation film ofthe invention.

An ultraviolet absorber such as, e.g., a benzotriazole, benzophenone,triazine, or benzoate ultraviolet absorber may be incorporated accordingto need.

The optical compensation film of the invention may be one which containsother ingredients such as a polymer, surfactant, polymer electrolyte,conductive complex, inorganic filler, pigment, dye, antistatic agent,antiblocking agent, and lubricant, as long as this is not counter to thespirit of the invention.

After having been laminated to a polarizer, the optical compensationfilm of the invention can be used as a circularly or ellipticallypolarizing plate. The optical compensation film of the invention isuseful also as optical compensation films such as aviewing-angle-improving film and color compensation film forliquid-crystal display elements. The circularly polarizing plate may beused as an antireflection film. Furthermore, the optical compensationfilm can be used as an optical compensation film for improving theviewing-angle characteristics of a brightness-improving film for use inliquid-crystal displays.

The retardation film of the invention is explained next.

Examples of the fumaric ester resin to be used for the retardation filmof the invention include polymers of fumaric esters. Preferred of theseis a fumaric ester resin comprising at least 50% by mole fumaric diesterresidue units represented by general formula (a) given above.

The retardation film of the invention is a retardation film whichcomprises the fumaric ester resin and need not contain fine particles.

The retardation film of the invention is a retardation film which ischaracterized in that when the refractive index in a fast-axis directionof the film plane, the refractive index in an in-plane directionperpendicular to the fast-axis direction, and the refractive index in anout-of-plane vertical direction are expressed by nx, ny, and nz,respectively, the refractive indexes satisfy the relationship nx<ny≦nz.Since this retardation film satisfies the relationship nx<ny≦nz, itshows the excellent ability to compensate the viewing-anglecharacteristics of STN-LCDs, IPS-LCDs, reflection type LCDs,semi-transmissive LCDs, and the like.

From the standpoint of enabling the retardation film of the invention tobe a retardation film having better optical properties, the in-planeretardation (Re) thereof, as measured at a wavelength of 550 nm andrepresented by expression (2) given above, is preferably 50-2,000 nm,especially preferably 50-1,000 nm, even more preferably 100-500 nm.

With respect to greater details of the in-plane retardation (Re), whenthe retardation film of the invention is for use as a retardation filmfor viewing angle compensation in liquid-crystal displays working in theTN, VA, IPS, or OCB mode, then the in-plane retardation (Re) thereof ispreferably 50 nm or larger, especially preferably 100 nm or larger, evenmore preferably 135 nm or larger.

In the case where the retardation film is to be used as a circularlypolarizing film obtained by laminating and uniting the retardation filmto a polarizer, then the in-plane retardation (Re) of the film ispreferably 100-200 nm. Besides being used as a compensation film forreflection type liquid-crystal displays, the circularly polarizing filmis useful as an antireflection film, brightness-improving film, and thelike for organic EL displays or the like.

Furthermore, when the retardation film of the invention is to be used asa half-wave film, the in-plane retardation (Re) is preferably 200-400nm. When it is to be used for viewing angle compensation for abrightness-improving film for liquid-crystal displays working in the STNmode, the in-plane retardation (Re) thereof is preferably 50-1,000 nm.

The wavelength dependence of retardation can be expressed by the ratioof the retardation as measured at a wavelength of 450 nm (R450) to theretardation as measured at a wavelength of 550 nm (R550), i.e., theratio R450/R550. In the retardation film of the invention, the value ofR450/R550 is preferably 1.1 or lower, especially preferably 1.08 orlower, even more preferably 1.05 or lower.

The thickness of the retardation film is in the range of preferably10-400 μm, especially preferably 20-150 μm, even more preferably 30-100μm.

Processes for producing the retardation film of the invention are notparticularly limited. For example, a process may be used in which a filmis formed by, e.g., the solution casting method or melt casting methodused for producing the optical compensation film given above and thisfilm is stretched uniaxially or biaxially, whereby the retardation filmof the invention which has a regulated retardation can be obtained.Examples of techniques for uniaxial stretching include free-widthuniaxial stretching, stretching with a tenter, and stretching betweenrolls. Examples of techniques for biaxial stretching include stretchingwith a tenter and stretching by swelling into a tube form. Conditionsfor the stretching include a stretching temperature of preferably80-250° C., especially preferably 120-220° C., and a stretch ratio ofpreferably 1.01-5, especially preferably 1.01-2, because such conditionsare less apt to cause thickness unevenness and the retardation film thusobtained is excellent in mechanical properties and optical properties.

It is preferred that an antioxidant should have been incorporated in theretardation film of the invention in order to enhance thermal stabilitynecessary for film formation and the thermal stability of theretardation film itself. Examples of the antioxidant includehindered-phenol antioxidants, phosphorus compound antioxidants, andother antioxidants. These antioxidants may be used alone or incombination of two or more thereof. It is preferred to use a combinationof a hindered-phenol antioxidant and a phosphorus compound antioxidantbecause it performs a synergistically improved antioxidant function. Inthis case, it is especially preferred to mix and use the twoingredients, for example, in such a proportion that the amount of thephosphorus compound antioxidant is 100-500 parts by weight per 100 partsby weight of the hindered-phenol antioxidant. The amount of theantioxidants to be added is in the range of preferably 0.01-10 parts byweight, especially preferably 0.5-1 part by weight, per 100 parts byweight of the fumaric ester resin constituting the retardation film ofthe invention.

An ultraviolet absorber such as, e.g., a benzotriazole, benzophenone,triazine, or benzoate ultraviolet absorber may be incorporated accordingto need.

The retardation film of the invention may be one which contains otheringredients such as a polymer, surfactant, polymer electrolyte,conductive complex, inorganic filler, pigment, dye, antistatic agent,antiblocking agent, and lubricant, as long as this is not counter to thespirit of the invention.

The retardation film of the invention may be a retardation film (film F)comprising: a film (C) which is a film comprising a fumaric ester resinand in which when the refractive index in a fast-axis direction of thefilm plane, the refractive index in an in-plane direction perpendicularto the fast-axis direction, and the refractive index in an out-of-planevertical direction are expressed by nx, ny, and nz, respectively, therefractive indexes satisfy the relationship nx<ny≦nz; and a film (D)which has three-dimensional refractive indexes satisfying therelationship ny>nx≧nz or ny>nz≧nx, wherein nx is the refractive index ina fast-axis direction of the film plane, ny is the refractive index inan in-plane direction perpendicular to the fast-axis direction, and nzis the refractive index in an out-of-plane vertical direction.

Examples of the fumaric ester resin to be used for film F includepolymers of fumaric esters. Preferred of these is a fumaric ester resincomprising at least 50% by mole fumaric diester residue unitsrepresented by general formula (a) given above.

Film (C) used in film F has an in-plane retardation (Re), as measured ata wavelength of 550 nm and represented by expression (2) given above,wherein d is the thickness of the film, of preferably 50-2,000 nm,especially 100-600 nm, more preferably 120-300 nm.

On the other hand, film (D) used in film F has an in-plane retardation(Re), as measured at a wavelength of 550 nm and represented byexpression (2) given above, of preferably 50-2,000 nm.

Film (D), which is a film having three-dimensional refractive indexessatisfying the relationship ny>nx≧nz or ny>nz≧nx, can be obtained, forexample, by uniaxially stretching a polymer having positivebirefringence or by laminating a heat-shrinkable film to one or eachside of a polymer having positive birefringence and then uniaxiallystretching the laminate. The polymers having positive birefringence arenot particularly limited as long as these are polymers having positivebirefringence. From the standpoints of heat resistance, transparency,etc., preferred examples of the polymers include polycarbonate resins,polyethersulfone resins, polyarylate resins, polyimide resins,polycycloolefin resins, and N-substituted maleimide resins. Preferred ofthese are films having high wavelength-dispersion characteristics, suchas films of polycarbonate resins and polyethersulfone resins. This isbecause such resins give a retardation film which especially has reversewavelength-dispersion characteristics.

In film F, which is a retardation film comprising film (C) and film (D),the angle formed by the fast-axis of film (C) and the fast-axis of film(D) can be set according to purposes. From the standpoints of regulationof wavelength-dispersion characteristics and productivity, that angle ispreferably in the range of 90°±20°, especially preferably in the rangeof 90°±5°, even more preferably 90°.

The in-plane retardation (Re) of the retardation film composed of film(C) and film (D) is the difference in retardation between film (C) andfilm (D). When this retardation film is to be used as a retardation filmhaving a quarter-wavelength retardation, i.e., as a so-calledquarter-wave plate, it is preferred that the difference between thein-plane retardation (Re) of film (C) and the in-plane retardation offilm (D) both measured at a wavelength of 550 nm should be 100-160 nm,especially 130-150 nm. When the retardation film is to be used as aretardation film having a half-wavelength retardation, i.e., as aso-called half-wave plate, it is preferred that the difference betweenthe in-plane retardation (Re) of film (C) and the in-plane retardationof film (D) both measured at a wavelength of 550 nm should be 250-300nm.

The wavelength-dispersion characteristics of film F can be controlled byregulating the retardations of film (C) and film (D). When film F is tobe used as a quarter-wave plate or half-wave plate, then the ratio ofthe retardation as measured at a wavelength of 450 nm (R450) to theretardation as measured at a wavelength of 550 nm (R550), i.e., theratio R450/R550, is preferably 1.0 or lower, especially preferably 0.99or lower, even more preferably 0.98 or lower. Furthermore, the ratio ofthe retardation as measured at a wavelength of 650 nm (R650) to theretardation as measured at a wavelength of 550 nm (R550), i.e., theratio R650/R550, is preferably 1.0 or higher, especially preferably 1.01or higher.

Processes for producing film (C) for use in film F are not particularlylimited. For example, a process may be used in which a film is formedby, e.g., the solution casting method or melt casting method used forproducing the optical compensation film given above and this film isstretched uniaxially or biaxially, whereby film (C) which has aregulated retardation and is for use in the retardation film of theinvention can be obtained.

Furthermore, processes for producing film (D) for use in film F are notparticularly limited. For example, use may be made of: a process inwhich a film is formed by, e.g., the solution casting method or meltcasting method used for producing the optical compensation film givenabove and this film is stretched uniaxially or biaxially; or a processin which a heat-shrinkable film is laminated to one or each side of thatfilm and this laminate is stretched uniaxially. Thus, film (D) which hasa regulated retardation and is for use in the retardation film of theinvention can be obtained.

Examples of techniques for uniaxial stretching include free-widthuniaxial stretching, stretching with a tenter, and stretching betweenrolls. Examples of techniques for biaxial stretching include stretchingwith a tenter and stretching by swelling into a tube form. Examples oftechniques for the uniaxial stretching after the laminating of aheat-shrinkable film include a method in which a heat-shrinkable film islaminated to each or one side of a polymer having positive birefringenceby means of adhesiveness of the film itself or with a bonding means,e.g., an easily strippable adhesive, and the resultant laminate issubjected to free-width uniaxial stretching, stretching with a tender,or stretching between rolls. The heat-shrinkable film is stripped offafter the stretching. Stretching conditions include a stretchingtemperature of preferably 80-250° C., especially preferably 120-220° C.,and a stretch ratio of preferably 1.01-5, especially preferably 1.01-2,because such conditions are less apt to cause thickness unevenness andthe retardation film thus obtained is excellent in mechanical propertiesand optical properties.

The heat-shrinkable film to be used is not particularly limited.Examples thereof include biaxially stretched films and uniaxiallystretched films. In particular, examples thereof include biaxiallystretched films and uniaxially stretched films of polyesters,polystyrene, polyethylene, polypropylene, poly(vinyl chloride), andpoly(vinylidene chloride).

Film F can be produced, for example, by laminating film (C) to film (D).Methods for the laminating are not particularly limited. Sheet-by-sheetlaminating is possible. It is especially preferred that film (C) andfilm (D) each in a roll-film form be laminated to each other with aknown adhesive or the like. The laminating is preferably conducted sothat the angle formed by the fast-axis of film (C) and the fast-axis offilm (D) is 90°±20°. That angle is preferably 90°±5°, more preferably90°, because such an angle can be attained by roll-to-roll laminating.

It is also possible to produce film F by molding unstretched films forfilm (C) and film (D) by coextrusion or another technique and thenstretching the laminate.

It is preferred that an antioxidant should have been incorporated infilm F in order to enhance thermal stability necessary for filmformation and the thermal stability of the retardation film itself.Examples of the antioxidant include hindered-phenol antioxidants,phosphorus compound antioxidants, and other antioxidants. Theseantioxidants may be used alone or in combination of two or more thereof.It is preferred to use a combination of a hindered-phenol antioxidantand a phosphorus compound antioxidant because it performs asynergistically improved antioxidant function. In this case, it isespecially preferred to mix and use the two ingredients, for example, insuch a proportion that the amount of the phosphorus compound antioxidantis 100-500 parts by weight per 100 parts by weight of thehindered-phenol antioxidant. The amount of the antioxidants to be addedis in the range of preferably 0.01-10 parts by weight, especiallypreferably 0.5-1 part by weight, per 100 parts by weight of the fumaricester resin constituting the retardation film of the invention.

An ultraviolet absorber such as, e.g., a benzotriazole, benzophenone,triazine, or benzoate ultraviolet absorber may be incorporated accordingto need.

Film F may be one which contains other ingredients such as a polymer,surfactant, polymer electrolyte, conductive complex, inorganic filler,pigment, dye, antistatic agent, antiblocking agent, and lubricant, aslong as this is not counter to the spirit of the invention.

Film F may be laminated to itself or to another retardation film.

Besides being used as a circularly polarizing film comprising aquarter-wave plate and a polarizer laminated and united thereto or as aretardation film for reflection type liquid-crystal displays, film F isuseful as an antireflection film, brightness-improving film, and thelike for organic EL displays, touch panels, or the like. Film F may belaminated to a polarizer to produce a composite polarizer.

EXAMPLES

The invention will be explained below in detail by reference toExamples, but the invention should not be construed as being limited bythe following Examples in any way. The reagents used were commercialproducts unless otherwise indicated.

Composition of Fumaric Diester Resin (Fumaric Diester Copolymer):

A nuclear magnetic resonance analyzer (trade name, JNM-GX270;manufactured by JEOL Ltd.) was used to determine the composition byproton nuclear magnetic resonance (¹H-NMR) spectroscopy.

Determination of Number-Average Molecular Weight:

A gel permeation chromatograph (GPC) (trade name, HLC-8020; manufacturedby Tosoh Corp.) equipped with a column (trade name, TSK-GEL GMH_(HR)-H;manufactured by Tosoh Corp.) was used to conduct an examination underthe conditions of a column temperature of 40° C. and a flow rate of 1.0mL/min using THF as a solvent. The molecular weight was determined as avalue calculated for standard polystyrene.

Measurement of Glass Transition Temperature (Tg):

A differential scanning calorimeter (trade name, DSC2000; manufacturedby Seiko Instruments Inc.) was used to make a measurement at a heatingrate of 10° C./min.

Measurement of Light Transmittance and Haze of Film:

The light transmittance and haze of a film produced were measured with ahaze meter (trade name, NDH2000; manufactured by Nippon DenshokuIndustries Co., Ltd.). The measurement of light transmittance and thatof haze were made in accordance with JIS K 7361-1 (1997) and JIS K 7136(2000), respectively.

Measurement of Refractive Index:

An Abbe refractometer (manufactured by ATAGO) was used to make ameasurement in accordance with JIS K 7142 (1981).

Measurement of Three-Dimensional Refractive Indexes and Calculation ofOut-Of-Plane Retardation, In-Plane Retardation, and OrientationParameter:

A sample inclination type automatic biretringence analyzer (trade name,KOBRA-WR; manufactured by Oji Scientific Instruments) was used tomeasure three-dimensional refractive indexes while changing the angle ofelevation. Furthermore, the out-of-plane retardation (Rth), in-planeretardation (Re), and orientation parameter (Nz) were calculated fromthe three-dimensional refractive indexes.

Judgment Concerning Positiveness/Negativeness of Birefringence;

Whether birefringence was positive or negative was judged using thepolarizing microscope described in K obunshi Sozai No Henk o Kenbiky oNy umon (Hiroshi Awaya, published by Agune Gijitsu Center, Chapter 5,pp. 78-82 (2001)).

Measurement of Modulus of Photoelasticity;

Measurement was made with an optical rheometer (HRS-100, manufactured byOak Mfg. Co.) at a pulling rate of 1%/s.

Synthesis Example 1 Production of Fumaric Diester Homopolymer

Into a 30-L autoclave were introduced 18 kg of distilled watercontaining 0.2% by weight partly saponified poly(vinyl alcohol), 3 kg ofdiisopropyl fumarate, and 7 g of dimethyl 2,2′-azobisisobutyrate as apolymerization initiator. Suspension radical polymerization reaction wasconducted under the conditions of a polymerization temperature of 50° C.and a polymerization time of 24 hours. The particles obtained were takenout by filtration, subsequently sufficiently washed with methanol, andthen dried at 80° C. to obtain a diisopropyl fumarate homopolymer. Thediisopropyl fumarate homopolymer obtained had a number-average molecularweight of 160,000.

Synthesis Example 2 Synthesis of Fumaric Diester Copolymer

Into a 30-L autoclave equipped with a stirrer, condenser, nitrogenintroduction tube, and thermometer were introduced 48 g of hydroxypropylmethyl cellulose (trade name, Metolose 60SH-50; manufactured byShin-Etsu Chemical Co., Ltd.), 15,601 g of distilled water, 8,161 g ofdiisopropyl fumarate, 240 g of 3-ethyl-3-oxetanylmethyl acrylate, and 45g of t-butyl peroxypivalate as a polymerization initiator. Nitrogenbubbling was conducted for 1 hour. Thereafter, the reaction mixture washeld at 49° C. for 24 hours with stirring at 200 rpm to thereby conductradical suspension polymerization. The autoclave was cooled to roomtemperature, and the suspension containing polymer particles yielded wascentrifuged. The polymer particles obtained were washed with distilledwater twice and with methanol twice and then vacuum-dried at 80° C.(yield: 80%).

The polymer particles obtained had a number-average molecular weight of142,000. It was ascertained through ¹H-NMR spectroscopy that the polymerparticles were a diisopropyl fumarate copolymer in which diisopropylfumarate residue units/3-ethyl-3-oxetanylmethyl acrylate residueunits=96/4 (mol %).

Synthesis Example 3 Synthesis of Fumaric Diester Copolymer

Into a 75-mL glass ampul were introduced 69.89 g of diisopropylfumarate, 0.91 g of 3-ethyl-3-oxetanylmethyl acrylate, and 0.39 g oft-butyl peroxypivalate as a polymerization initiator. After nitrogendisplacement, the ampul was evacuated and sealed. The contents were heldat 50° C. for 24 hours to thereby conduct radical polymerization. Thepolymer yielded was cooled to room temperature and then dissolved intetrahydrofuran. The polymer solution obtained was added to an excess ofmethanol to thereby obtain a polymer as a white powder. The polymerobtained was washed with methanol three times and then vacuum-dried at80° C. (yield: 84%).

The polymer obtained had a number-average molecular weight of 171,000.It was ascertained through ¹H-NMR spectroscopy that the polymer was adiisopropyl fumarate copolymer in which diisopropyl fumarate residueunits/3-ethyl-3-oxetanylmethyl acrylate residue units=98/2 (mol %).

Synthesis Example 4 Synthesis of Fumaric Diester Copolymer

Into a 75-mL glass ampul were introduced 68.09 g of diisopropylfumarate, 3.06 g of 3-ethyl-3-oxetanylmethyl acrylate, and 0.39 g oft-butyl peroxypivalate as a polymerization initiator. After nitrogendisplacement, the ampul was evacuated and sealed. The contents were heldat 50° C. for 24 hours to thereby conduct radical polymerization. Thepolymer yielded was cooled to room temperature and then dissolved intetrahydrofuran. The polymer solution obtained was added to an excess ofmethanol to thereby obtain a polymer as a white powder. The polymerobtained was washed with methanol three times and then vacuum-dried at80° C. (yield: 70%).

The polymer obtained had a number-average molecular weight of 179,000.It was ascertained through ¹H-NMR spectroscopy that the polymer was adiisopropyl fumarate copolymer in which diisopropyl fumarate residueunits/3-ethyl-3-oxetanylmethyl acrylate residue units ˜94/6 (mol %).

Film Production Example 1

The diisopropyl fumarate homopolymer obtained in Synthesis Example 1 wasdissolved in THF to obtain a 22% solution. Thereto were added 0.35 partsby weight of tris(2,4-di-t-butylphenyl) phosphite as a hindered-phenolantioxidant, 0.15 parts by weight of pentaerythritoltetrakis(3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate) as aphosphorus-compound antioxidant, and 1 part by weight of2-(2H-benzotriazol-2-yl)-p-cresol as an ultraviolet absorber per 100parts by weight of the diisopropyl fumarate homopolymer. The resultantcomposition was cast on the supporting base of a solution castingapparatus by the T-die method and dried for 15 minutes at each of 40°C., 80° C., and 120° C. Thus, a film having a width of 250 mm and athickness of 120 μm was obtained.

The film obtained had a light transmittance of 93%, haze of 0.3%, andrefractive index of 1.470.

Film Production Example 2

The diisopropyl fumarate homopolymer obtained in Synthesis Example 1 wasdissolved in THF to obtain a 22% solution. Thereto were added 0.35 partsby weight of tris(2,4-di-t-butylphenyl) phosphite as a hindered-phenolantioxidant, 0.15 parts by weight of pentaerythritoltetrakis(3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate) as aphosphorus-compound antioxidant, and 1 part by weight of2-(2H-benzotriazol-2-yl) p-cresol as an ultraviolet absorber per 100parts by weight of the diisopropyl fumarate homopolymer. The resultantcomposition was cast on the supporting base of a solution castingapparatus by the T-die method and dried for 10 minutes at each of 40°C., 80° C., and 120° C. Thus, a film having a width of 250 mm and athickness of 105 μm was obtained.

The film obtained had a light transmittance of 93%, haze of 0.3%, andrefractive index of 1.470.

Film Production Example 3

The diisopropyl fumarate homopolymer obtained in Synthesis Example 1 wasdissolved in THF to obtain a 22% solution. This solution was cast on thesupporting base of a solution casting apparatus by the T-die method inthe same manner as in Film Production Example 1. Thus, a film having awidth of 250 mm and a thickness of 124 μm was obtained.

The film obtained had a light transmittance of 93%, haze of 0.3%, andrefractive index of 1.470.

Film Production Example 4

A polycarbonate resin (manufactured by Aldrich) was dissolved inmethylene chloride to obtain a 25% solution. Thereto were added 0.35parts by weight of tris(2,4-di-t-butylphenyl) phosphite and 0.15 partsby weight of pentaerythritoltetrakis(3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate) as antioxidantsand 1 part by weight of 2-(2H-benzotriazol-2-yl)-p-cresol as anultraviolet absorber per 100 parts by weight of the polycarbonate resin.The resultant composition was cast on the supporting base of a solutioncasting apparatus by the T-die method and dried for 15 minutes at eachof 40° C., 80° C., and 120° C. Thus, a film having a width of 250 mm anda thickness of 100 μm was obtained.

The film obtained had a light transmittance of 91%, haze of 0.6%, andrefractive index of 1.583.

Film Production Example 5

A polycycloolefin resin (polynorbonene having ester groups; manufacturedby Aldrich) was dissolved in methylene chloride to obtain 25% solution.Thereto were added 0.35 parts by weight of tris(2,4-di-t-butylphenyl)phosphite and 0.15 parts by weight of pentaerythritoltetrakis(3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate) as antioxidantsand 1 part by weight of 2-(2H-benzotriazol-2-yl)-p-cresol as anultraviolet absorber per 100 parts by weight of the polycycloolefinresin. The resultant composition was cast on the supporting base of asolution casting apparatus by the T-die method and dried for 15 minutesat each of 40° C., 80° C., and 120° C. Thus, a film having a width of250 mm and a thickness of 100 μm was obtained.

The film obtained had a light transmittance of 92%, haze of 0.4%, andrefractive index of 1.510.

Film Production Example 6

A polycarbonate resin (manufactured by Aldrich) was dissolved inmethylene chloride to obtain a 25% solution. A film having a width of250 mm and a thickness of 85 μm was obtained therefrom in the samemanner as in Film Production Example 2.

The film obtained had a light transmittance of 91%, haze of 0.5%, andrefractive index of 1.583.

Example 1

The diisopropyl fumarate homopolymer obtained in Synthesis Example 1 wasdissolved in THF to obtain a 22% solution. Thereto were added 0.35 partsby weight of tris(2,4-di-t-butylphenyl) phosphite as a hindered-phenolantioxidant, 0.15 parts by weight of pentaerythritoltetrakis(3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate) as aphosphorus-compound antioxidant, and 1 part by weight of2-(2H-benzotriazol-2-yl)-p-cresol as an ultraviolet absorber per 100parts by weight of the diisopropyl fumarate homopolymer. The resultantcomposition was cast on the supporting base of a solution castingapparatus by the T-die method and dried for 15 minutes at each of 40°C., 80° C., and 120° C. Thus, a film having a width of 250 mm and athickness of 21 μm was obtained.

The film obtained had a light transmittance of 93%, haze of 0.3%, andmodulus of photoelasticity of 5×10⁻¹² Pa⁻¹. The three-dimensionalrefractive indexes of the film were: nx=1.4689, ny=1.4689, and nz=1.4723(nz>ny=nx). The film obtained had an in-plane retardation (Re) of 0 nmand an out-of-plane retardation (Rth) of −71 nm. The retardation ratio(R450/R550) (wavelength dependence) thereof was 1.02. Furthermore, thefilm obtained had a tensile strength of 50 MPa and a tensile elongationof 12%. It had sufficiently practical mechanical properties.

Those results show that the film obtained had a high thickness-directionrefractive index and a small wavelength dependence and was hencesuitable for use as an optical compensation film.

Example 2

A film having a width of 250 mm and a thickness of 30 μm was obtained inthe same manner as in Example 1.

The film obtained had a light transmittance of 93% and a haze of 0.4%.The three-dimensional refractive indexes of the film were: nx=1.4690,ny=1.4690, and nz=1.4721 (nz>ny=nx). The film obtained had an in-planeretardation (Re) of 0 nm and an out-of-plane retardation (Rth) of −93nm. The retardation ratio (R450/R550) (wavelength dependence) thereofwas 1.02.

Those results show that the film obtained had a high thickness-directionrefractive index and a small wavelength dependence and was hencesuitable for use as an optical compensation film.

Example 3

The diisopropyl fumarate copolymer obtained in Synthesis Example 2 wasdissolved in a solvent composed of toluene and methyl ethyl ketone in aweight ratio of 1:1 to obtain a 20% solution. This solution was cast onthe supporting base of a solution casting apparatus by the T-die methodand dried for 10 minutes at each of 80° C. and 120° C. Thus, a filmhaving a width of 250 mm and a thickness of 23 μm was obtained.

The film obtained had a light transmittance of 94%, haze of 0.3%, andmodulus of photoelasticity of 5×10⁻¹² Pa⁻¹. The three-dimensionalrefractive indexes of the film were: nx=1.4689, ny=1.4690, and nz=1.4721(nz>ny≈nx). The film obtained had an in-plane retardation (Re) of 1 nmand an out-of-plane retardation (Rth) of −87 nm. The retardation ratio(R450/R550) (wavelength dependence) thereof was 1.02. Furthermore, thefilm obtained had a tensile strength of 50 MPa and a tensile elongationof 11%. It had sufficiently practical mechanical properties.

Those results show that the film obtained had a high thickness-directionrefractive index and a small wavelength dependence and was hencesuitable for use as an optical compensation film.

Example 4

The diisopropyl fumarate copolymer obtained in Synthesis Example 3 wasdissolved in a solvent composed of toluene and methyl ethyl ketone in aweight ratio of 1:1 to obtain a 20% solution. This solution was cast onthe supporting base of a solution casting apparatus by the T-die methodand dried for 10 minutes at each of 80° C. and 120° C. Thus, a filmhaving a width of 250 mm and a thickness of 31 μm was obtained.

The film obtained had a light transmittance of 94%, haze of 0.3%, andmodulus of photoelasticity of 5×10⁻¹² Pa⁻¹. The three-dimensionalrefractive indexes of the film were: nx=1.4686, ny=1.4687, and nz=1.4727(nz>ny≈nx). The film obtained had an in-plane retardation (Re) of 1 nmand an out-of-plane retardation (Rth) of −127 nm. The retardation ratio(R450/R550) (wavelength dependence) thereof was 1.02. Furthermore, thefilm obtained had a tensile strength of 50 MPa and a tensile elongationof 11%. It had sufficiently practical mechanical properties.

Those results show that the film obtained had a high thickness-directionrefractive index and a small wavelength dependence and was hencesuitable for use as an optical compensation film.

Example 5

The diisopropyl fumarate copolymer obtained in Synthesis Example 4 wasdissolved in a solvent composed of toluene and methyl ethyl ketone in aweight ratio of 1:1 to obtain a 20% solution. This solution was cast onthe supporting base of a solution casting apparatus by the T-die methodand dried for 10 minutes at each of 80° C. and 120° C. Thus, a filmhaving a width of 250 mm and a thickness of 27 μm was obtained.

The film obtained had a light transmittance of 94%, haze of 0.3%, andmodulus of photoelasticity of 5×10⁻¹² Pa⁻¹. The three-dimensionalrefractive indexes of the film were; nx=1.4687, ny=1.4687, and nz=1.4726(nz>ny=nx). The film obtained had an in-plane retardation (Re) of 1 nmand an out-of-plane retardation (Rth) of −104 nm. The retardation ratio(R450/R550) (wavelength dependence) thereof was 1.02. Furthermore, thefilm obtained had a tensile strength of 50 MPa and a tensile elongationof 12%. It had sufficiently practical mechanical properties.

Those results show that the film obtained had a high thickness-directionrefractive index and a small wavelength dependence and was hencesuitable for use as an optical compensation film.

Comparative Example 1

A methylene chloride solution composed of 25% by weight polycarbonate(trade name, Panlite L1225; manufactured by Teijin Ltd.) and 75% byweight methylene chloride was prepared. This methylene chloride solutionwas cast on a poly(ethylene terephthalate) film, solidified byvolatilizing the solvent, and stripped off to thereby obtain a film. Thefilm thus obtained after stripping was further dried at 100° C. for 4hours and subsequently at 110° C., 120° C., and 130° C. each for 1 hourand then dried in a vacuum dryer at 120° C. for 4 hours. Thus, a filmhaving a thickness of about 90 μm (hereinafter referred to as film (1))was obtained.

The film (1) obtained had a glass transition temperature (Tg) of 150° C.It had a light transmittance of 90.0% and a haze of 0.6%. Thethree-dimensional refractive indexes of the film were; nx=1.5830,ny=1.5830, and nz=1.5830. The film obtained had an in-plane retardation(Re) of 0 nm and an out-of-plane retardation (Rth) of 0 nm.

Those results show that the film obtained did not have a highthickness-direction refractive index and was not suitable for use as anoptical compensation film.

Example 6

The film obtained in Comparative Example 1 was cut into a square havinga side length of 50 mm. This cut piece was stretched by +50% free-widthuniaxial stretching with a biaxially stretching apparatus (manufacturedby Imoto Seisakusho) under the conditions of a temperature of 170° C.and a stretching speed of 10 mm/min. The film stretched (referred to asfilm 1(a)) showed positive birefringence. The three-dimensionalrefractive indexes of the film 1(a) obtained were: nx=1.5826, ny=1.5842,and nz=1.5822 (ny>nx>nz). The in-plane retardation (Re) thereof was 125nm.

Furthermore, the film produced in Example 1 was laminated to the film1(a) to obtain a film having a thickness of 97 μm. The three-dimensionalrefractive indexes of this film were: nx=1.5593, ny=1.5606, andnz=1.5600. This film had an in-plane retardation (Re) of 126 nm and anorientation parameter (Nz) of 0.5.

Those results show that the film obtained was suitable for use as anoptical compensation film.

Example 7

The film obtained in Comparative Example 1 was cut into a square havinga side length of 50 mm. This cut piece was stretched by +33% free-widthuniaxial stretching with a biaxially stretching apparatus (manufacturedby Imoto Seisakusho) under the conditions of a temperature of 170° C.and a stretching speed of 10 mm/min. The film stretched (referred to asfilm 1(b)) showed positive birefringence. The three-dimensionalrefractive indexes of the film 1(b) obtained were: nx=1.5826, ny=1.5839,and nz=1.5825 (ny>nx>nz). The in-plane retardation (Re) thereof was 113nm.

Furthermore, the film produced in Example 2 was laminated to the film1(b) to obtain a film having a thickness of 113 μm. Thethree-dimensional refractive indexes of this film were: nx=1.5494,ny=1.5504, and nz=1.5502. This film had an in-plane retardation (Re) of113 nm and an orientation parameter (Nz) of 0.20.

Those results show that the film obtained was suitable for use as anoptical compensation film.

Coating Solution Production Example 1

The diisopropyl fumarate homopolymer obtained in Synthesis Example 1 wasdissolved in a solvent composed of toluene and methyl ethyl ketone in aweight ratio of 1:1 to obtain a 10% solution. Thereto were added 0.35parts by weight of tris(2,4-di-t-butylphenyl) phosphite and 0.15 partsby weight of pentaerythritoltetrakis(3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate) as antioxidantsand 1 part by weight of 2-(2H-benzotriazol-2-yl)-p-cresol as anultraviolet absorber per 100 parts by weight of the diisopropyl fumaratehomopolymer. Thus, a coating solution was obtained.

Example 8

The coating solution described above was applied by the doctor blademethod to the film 1(a) obtained in Example 6 in such an amount as toresult in a thickness on a dry basis (thickness of the layer made of thefumaric ester resin) of 21 μm to obtain a film (film thickness: 96 μm).The three-dimensional refractive indexes of the layer made of thefumaric ester resin were: nx=1.4689, ny=1.4689, and nz=1.4723(nz>ny=nx).

The three-dimensional refractive indexes of the film were; nx=1.5593,ny=1.5606, and nz=1.5600. This film had an in-plane retardation (Re) of125 nm and an orientation parameter (Nz) of 0.5.

Those results show that the film obtained was suitable for use as anoptical compensation film.

Example 9

The coating solution described above was applied by the doctor blademethod to the film 1(b) obtained in Example 7 in such an amount as toresult in a thickness on a dry basis (thickness of the layer made of thefumaric ester resin) of 30 μm to obtain a film (film thickness: 112 μm).The three-dimensional refractive indexes of the layer made of thefumaric ester resin were: nx=1.4690, ny=1.4690, and nz=1.4721(nz>ny=nx).

The three-dimensional refractive indexes of the film were: nx=1.5494,ny=1.5504, and nz=1.5502. This film had an in-plane retardation (Re) of112 nm and an orientation parameter (Nz) of 0.20.

Those results show that the film obtained was suitable for use as anoptical compensation film.

Example 10

The film obtained in comparative Example 1 was cut into a square havinga side length of 50 mm. This cut piece was stretched by +50% free-widthuniaxial stretching with a biaxially stretching apparatus (manufacturedby Imoto Seisakusho) under the conditions of a temperature of 165° C.and a stretching speed of 20 mm/min. The film stretched (referred to asfilm 1(c)) showed positive birefringence. The three-dimensionalrefractive indexes of the film 1(c) obtained were: nx=1.5820, ny=1.5851,and nz=1.5819 (ny>nx>nz). The in-plane retardation (Re) thereof was 263nm.

Furthermore, the coating solution described above was applied by thedoctor blade method to the film 1(c) to obtain a film (film thickness:94 μm). The three-dimensional refractive indexes of the layer made ofthe fumaric ester resin were: nx=1.4678, ny=1.4678, and nz=1.4744(nz>ny=nx).

The three-dimensional refractive indexes of the film were: nx=1.5089,ny=1.5117, and nz=1.5094. This film had an in-plane retardation (Re) of263 nm and an orientation parameter (Nz) of 0.82.

Those results show that the film obtained was suitable for use as anoptical compensation film.

Example 11

The film obtained in Comparative Example 1 was cut into a square havinga side length of 50 mm. This cut piece was stretched by +50% free-widthuniaxial stretching with a biaxially stretching apparatus (manufacturedby Imoto Seisakusho) under the conditions of a temperature of 160° C.and a stretching speed of 20 mm/min. The film stretched (referred to asfilm 1(d)) showed positive birefringence. The film 1(d) obtained had athickness of 83 μm and the three-dimensional refractive indexes thereofwere: nx=1.5813, ny=1.5865, and nz=1.5812 (ny>nx>nz). The in-planeretardation (Re) thereof was 429 nm.

Furthermore, the coating solution described above was applied by thedoctor blade method to the film 1(d) to obtain a film (film thickness;113 μm). The layer made of the fumaric ester resin had a thickness of 30μm and three-dimensional refractive indexes thereof were: nx=1.4690,ny=1.4690, and nz=1.4721 (nz>ny=nx).

The three-dimensional refractive indexes of the film were: nx=1.5484,ny=1.5522, and nz=1.5494, This film had an in-plane retardation (Re) of429 nm and an orientation parameter (Nz) of 0.74.

Those results show that the film obtained was suitable for use as anoptical compensation film.

Example 12

The film obtained in Comparative Example 1 was cut into a square havinga side length of 50 mm. This cut piece was stretched by +60% free-widthuniaxial stretching with a biaxially stretching apparatus (manufacturedby Imoto Seisakusho) under the conditions of a temperature of 170° C.and a stretching speed of 10 mm/min. The film stretched (referred to asfilm 1(e)) showed positive birefringence. The film 1(e) obtained had athickness of 70 μm and the three-dimensional refractive indexes thereofwere nx=1.5824, ny=1.5843, and nz=11.5823 (ny>nx>nz). The in-planeretardation (Re) thereof was 133 nm.

Furthermore, the coating solution described above was applied by thedoctor blade method to the film 1(e) to obtain a film (film thickness:113 μm). The three-dimensional refractive indexes of the film were:nx=1.5493, ny=1.5503, and nz=1.5504. This film had an in-planeretardation (Re) of 131 nm and an orientation parameter (Nz) of −0.10.

Those results show that the film obtained was suitable for use as anoptical compensation film.

Example 13

The film obtained in Comparative Example 1 was cut into a square havinga side length of 50 mm. This cut piece was stretched by +65% free-widthuniaxial stretching with a biaxially stretching apparatus (manufacturedby Imoto Seisakusho) under the conditions of a temperature of 170° C.and a stretching speed of 10 mm/min. The film stretched (referred to asfilm 1(f)) showed positive birefringence. The three-dimensionalrefractive indexes of the film 1(f) obtained were: nx=1.5825, ny=1.5843,and nz=1.5821 (ny>nx>nz). The in-plane retardation (Re) thereof was 137nm.

Furthermore, the film produced in Example 3 was laminated to the film1(f) to obtain a film having a thickness of 99 μm. The three-dimensionalrefractive indexes of the film were; nx=1.5523, ny=1.5537, andnz=1.5530. This film had an in-plane retardation (Re) of 137 nm and anorientation parameter (Nz) of 0.5.

Those results show that the film obtained was suitable for use as anoptical compensation film.

Comparative Example 2

The film obtained in Comparative Example 1 was cut into a square havinga side length of 50 mm. This cut piece was stretched by +50% free-widthuniaxial stretching with a biaxially stretching apparatus (manufacturedby Imoto Seisakusho) under the conditions of a temperature of 165° C.and a stretching speed of 10 mm/min (film thickness: 85 μm). The filmstretched showed positive birefringence and had an in-plane retardation(Re) of 264 μm. The three-dimensional refractive indexes of the filmwere; nx=1.5820, ny=1.5851, and nz=1.5819. This film had an orientationparameter (Nz) of 1.02.

Those results show that the film obtained did not have a highthickness-direction refractive index and was not suitable for use as anoptical compensation film.

Comparative Example 3

In a nitrogen atmosphere, 9.0 g of poly(2-vinylnaphthalane)(manufactured by Aldrich; weight-average molecular weight, 175,000) wasadded to 49.6 g of methylene chloride and this mixture was treated atroom temperature with a small Disper at 2,500 rpm for 1 hour to dissolvethe polymer. The polymer solution obtained was filtered through a 25-μmfilter. Subsequently, this polymer solution was applied by the barcoater method to a PET film having a thickness of 188 μm and thenair-dried overnight in a nitrogen stream. Thus, a film ofpoly(2-vinylnaphthalane) was formed on the PET substrate.

Part of this poly(2-vinylnaphthalane) film was peeled from the PETsubstrate and examined for film thickness and optical properties. Thethickness of the film dried was 58 μm. During the peeling, the filmpartly broke because of its brittleness.

The three-dimensional refractive indexes of the film obtained were:nx=1.6557, ny=1.6558, and nz=1.6578. The film had an out-of-planeretardation (Rth) of −120.2 nm and a retardation ratio (R450/R550)(wavelength dependence) of 1.12.

Those results show that the film obtained had a large wavelengthdependence although satisfying the relationship nz>ny≧nx and was henceunsuitable for use as an optical compensation film.

Comparative Example 4

To N-methyl-2-pyrrolidone (NMP) was added 13.2 g ofpoly(9-vinylcarbazole) (manufactured by Aldrich; weight-averagemolecular weight, about 1,100,000). This mixture was treated at roomtemperature with a small Disper at 6,000 rpm for 1 hour to dissolve thepolymer. The polymer solution obtained was filtered through a 25-mfilter. Subsequently, this polymer solution was applied by the barcoater method to a PET film having a thickness of 188 μm and thensubjected to hot-air drying at 60° C. for 1 hour and at 100° C. for 15minutes. Thus, a film of poly(9-vinylcarbazole) was formed on the PETsubstrate.

Part of this poly(9-vinylcarbazole) film was peeled from the PETsubstrate and examined for film thickness and optical properties. Thethickness of the film dried was 33 μm. During the peeling, the filmpartly broke because of its brittleness.

The three-dimensional refractive indexes of the film obtained were;nx=1.6819, ny=1.6820, and nz=1.6926. The film had an out-of-planeretardation (Rth) of −350.0 nm and a retardation ratio (R450/R550)(wavelength dependence) of 1.14.

Those results show that the film obtained had a large wavelengthdependence although satisfying the relationship nz>ny≧nx and was henceunsuitable for use as an optical compensation film.

Example 14

The film obtained in Film Production Example 1 was cut into a squarehaving a side length of 50 mm. This cut piece was stretched byfree-width uniaxial stretching in a stretch ratio of 1.125 with abiaxially stretching apparatus (manufactured by Imoto Seisakusho) underthe conditions of a temperature of 140° C. and a stretching speed of 10mm/min. The film stretched was examined for three-dimensional refractiveindexes. As a result, the film had a low refractive index in thestretching axis direction. The film obtained was hence found to havenegative birefringence.

From the results of the examination for three-dimensional refractiveindexes (nx=1.4681, ny=1.4692, and nz=1.4727), the film obtained wasfound to satisfy the relationship nx<ny<nz and have a high refractiveindex in the film thickness direction. The film had an in-planeretardation Re (Re=(ny−nx)×d) as large as 131 nm. It had a retardationratio (R450/R550) (wavelength dependence) as low as 1.02.

Those results show that the film obtained had negative birefringence, ahigh thickness-direction refractive index, a large in-plane retardation,and a small wavelength dependence. The film was hence found to besuitable for use as a retardation film.

Example 15

The film obtained in Film Production Example 1 was cut into a squarehaving a side length of 50 mm. This cut piece was stretched byfree-width uniaxial stretching in a stretch ratio of 1.25 with abiaxially stretching apparatus (manufactured by Imoto Seisakusho) underthe conditions of a temperature of 140° C. and a stretching speed of 100mm/min. The film stretched was examined for three-dimensional refractiveindexes. As a result, the film had a low refractive index in thestretching axis direction. The film obtained was hence found to havenegative birefringence.

From the results of the examination for three-dimensional refractiveindexes (nx=1.4667, ny=1.4704, and nz=1.4729), the film obtained wasfound to satisfy the relationship nx<ny<nz and have a high refractiveindex in the film thickness direction. The film had an in-planeretardation Re (Re=(ny−nx)×d) as large as 418 nm. It had a retardationratio (R450/R550) (wavelength dependence) as low as 1.02.

Those results show that the film obtained had negative birefringence, ahigh thickness-direction refractive index, a large in-plane retardation,and a small wavelength dependence. The film was hence found to besuitable for use as a retardation film.

Example 16

The film obtained in Film Production Example 1 was cut into a squarehaving a side length of 50 mm. This cut piece was stretched byfree-width uniaxial stretching in a stretch ratio of 1.375 with abiaxially stretching apparatus (manufactured by Imoto Seisakusho) underthe conditions of a temperature of 140° C. and a stretching speed of 10mm/min. The film stretched was examined for three-dimensional refractiveindexes. As a result, the film had a low refractive index in thestretching axis direction. The film obtained was hence found to havenegative birefringence.

From the results of the examination for three-dimensional refractiveindexes (nx=1.4653, ny=1.4714, and nz=1.4733), the film obtained wasfound to satisfy the relationship nx<ny<nz and have a high refractiveindex in the film thickness direction. The film had an in-planeretardation Re (Re=(ny−nx)×d) as large as 636 nm. It had a retardationratio (R450/R550) (wavelength dependence) as low as 1.02.

Those results show that the film obtained had negative birefringence, ahigh thickness-direction refractive index, a large in-plane retardation,and a small wavelength dependence. The film was hence found to besuitable for use as a retardation film.

Comparative Example 5

The film obtained in Film Production Example 4 was cut into a squarehaving a side length of 50 mm. This cut piece was stretched byfree-width uniaxial stretching in a stretch ratio of 1.10 with abiaxially stretching apparatus (manufactured by Imoto Seisakusho) underthe conditions of a temperature of 170° C. and a stretching speed of 10mm/min. The film stretched was examined for three-dimensional refractiveindexes. As a result, the film had a low refractive index in thedirection perpendicular to the stretching axis direction. The filmobtained was hence found to have positive birefringence.

From the results of the examination for three-dimensional refractiveindexes (nx=1.5844, ny=1.5823, and nz=1.5823), the film obtained wasfound to satisfy the relationship nx>ny=nz and not to have a highrefractive index in the film thickness direction.

Those results show that the film obtained was not suitable for use as aretardation film having the ability to compensate the viewing-anglecharacteristics of STN-LCDs and IPS-LCDs.

Comparative Example 6

The film obtained in Film Production Example 5 was cut into a squarehaving a side length of 50 mm. This cut piece was stretched byfree-width uniaxial stretching in a stretch ratio of 2.0 with abiaxially stretching apparatus (manufactured by Imoto Seisakusho) underthe conditions of a temperature of 180° C. and a stretching speed of 15mm/min. The film stretched was examined for three-dimensional refractiveindexes. As a result, the film had a low refractive index in thedirection perpendicular to the stretching axis direction. The filmobtained was hence found to have positive birefringence.

From the results of the examination for three-dimensional refractiveindexes (nx=1.5124, ny=1.5090, and nz=1.5090), the film obtained wasfound to satisfy the relationship nx>ny=nz and not to have a highrefractive index in the film thickness direction.

Those results show that the film obtained was not suitable for use as aretardation film having the ability to compensate the viewing-anglecharacteristics of STN-LCDs and IPS-LCDs.

Example 17

The film obtained in Film Production Example 2 was cut into a squarehaving a side length of 50 mm. This cut piece was stretched byfree-width uniaxial stretching in a stretch ratio of 1.2 with abiaxially stretching apparatus (manufactured by Imoto Seisakusho) underthe conditions of a temperature of 140° C. and a stretching speed of 10mm/min (hereinafter referred to as film A-1). The film stretched wasexamined for three-dimensional refractive indexes. From the results ofthe examination (nx=1.4673, ny=1.4702, and nz=1.4725) (nx<ny<nz), thefilm obtained was found to have a low refractive index in the stretchingaxis direction and have negative birefringence. The film had an in-planeretardation Re (Re=(ny−nx)×d) of 283 nm.

The polycarbonate film obtained in Film Production Example 4 was cutinto a square having a side length of 50 mm. This cut piece wasstretched by free-width uniaxial stretching in a stretch ratio of 1.5with a biaxially stretching apparatus (manufactured by Imoto Seisakusho)under the conditions of a temperature of 170° C. and a stretching speedof 10 mm/min (hereinafter referred to as film B-1). Thethree-dimensional refractive indexes of the film obtained were:nx=1.5827, ny=1.5842, and nz=1.5827 (ny>nz=nx). It showed positivebirefringence. This film had an in-plane retardation (Re) of 130 nm.

The film A-1 and film B-1 produced above were laminated to each other sothat the fast-axes thereof were perpendicular to each other (angle,90°). The laminated film had a thickness of 186 μm and an in-planeretardation (Re) of 153 nm. The ratio of the retardation as measured ata wavelength of 450 μm (R450) to the retardation as measured at awavelength of 550 nm (R550), i.e., the ratio R450/R550, was 0.98.Furthermore, the ratio of the retardation as measured at a wavelength of650 nm (R650) to the retardation as measured at a wavelength of 550 nm(R550), i.e., the ratio R650/R550, was 1.01.

Those results show that the obtained film had controlledwavelength-dispersion characteristics and reverse wavelength-dispersioncharacteristics and that it was hence suitable for use as a retardationfilm. It was suitable also as a retardation film having aquarter-wavelength retardation, i.e., as a so-called quarter-wave plate.

Example 18

The film obtained in Film Production Example 3 was cut into a squarehaving a side length of 50 mm. This cut piece was stretched byfree-width uniaxial stretching in a stretch ratio of 1.25 with abiaxially stretching apparatus (manufactured by Imoto Seisakusho) underthe conditions of a temperature of 160° C. and a stretching speed of 10mm/min (hereinafter referred to as film A-2). The film stretched wasexamined for three-dimensional refractive indexes. From the results ofthe examination (nx=1.4660, ny=1.4709, and nz=1.4731) (nx<ny<nz), thefilm obtained was found to have a low refractive index in the stretchingaxis direction and have negative birefringence. The film had an in-planeretardation Re (Re=(ny−nx)×d) of 531 nm.

The polycarbonate film obtained in Film Production Example 6 was cutinto a square having a side length of 50 mm. This cut piece wasstretched by free-width uniaxial stretching in a stretch ratio of 1.5with a biaxially stretching apparatus (manufactured by Imoto Seisakusho)under the conditions of a temperature of 160° C. and a stretching speedof 20 mm/min (hereinafter referred to as film B-2). Thethree-dimensional refractive indexes of the film obtained were:nx=1.5811, ny=1.5863, and nz=1.5819 (ny>nz>nx). It showed positivebirefringence. This film had an in-plane retardation (Re) of 395 nm.

The film A-2 and film B-2 produced above were laminated to each other sothat the fast-axes thereof were perpendicular to each other (angle,90°). The laminated film had a thickness of 185 μm and an in-planeretardation (Re) of 136 nm. The ratio of the retardation as measured ata wavelength of 450 nm (R450) to the retardation as measured at awavelength of 550 mm (R550), i.e., the ratio R450/R550, was 0.91.Furthermore, the ratio of the retardation as measured at a wavelength of650 nm (R650) to the retardation as measured at a wavelength of 550 nm(R550), i.e., the ratio R650/R550, was 1.07.

Those results show that the obtained film had controlledwavelength-dispersion characteristics and reverse wavelength-dispersioncharacteristics and that it was hence suitable for use as a retardationfilm. It was suitable also as a retardation film having aquarter-wavelength retardation, i.e., as a so-called quarter-wave plate.

Example 19

The film obtained in Film Production Example 6 was cut into a squarehaving a side length of 50 mm. This cut piece was stretched byfree-width uniaxial stretching in a stretch ratio of 1.5 with abiaxially stretching apparatus (manufactured by Imoto Seisakusho) underthe conditions of a temperature of 165° C. and a stretching speed of 20mm/min (hereinafter referred to as film B-3). The three-dimensionalrefractive indexes of the film obtained were; nx=1.5820, ny=1.5849, andnz=1.5819 (ny>nx>nz). It showed positive birefringence. This film had anin-plane retardation (Re) of 261 nm.

The film A-2 produced in Example 18 and the film B-3 produced above werelaminated to each other so that the fast-axes thereof were perpendicularto each other (angle, 90°). The laminated film had a thickness of 199 μmand an in-plane retardation (Re) of 270 nm. The ratio of the retardationas measured at a wavelength of 450 nm (R450) to the retardation asmeasured at a wavelength of 550 nm (R550), i.e., the ratio R450/R550,was 0.97. Furthermore, the ratio of the retardation as measured at awavelength of 650 nm (R650) to the retardation as measured at awavelength of 550 nm (R550), i.e., the ratio R650/R550, was 1.03.

Those results show that the obtained film had controlledwavelength-dispersion characteristics and reverse wavelength-dispersioncharacteristics and that it was hence suitable for use as a retardationfilm. It was suitable also as a retardation film having ahalf-wavelength retardation, i.e., as a so-called half-wave plate.

Example 20

A commercial PES film (manufactured by Lonza) was cut into a squarehaving a side length of 50 mm. This cut piece was stretched byfree-width uniaxial stretching in a stretch ratio of 1.5 with abiaxially stretching apparatus (manufactured by Imoto Seisakusho) underthe conditions of a temperature of 245° C. and a stretching speed of 20mm/min (hereinafter referred to as film B-4). The three-dimensionalrefractive indexes of the film obtained were: nx-1.6587, ny=1.6611, andnz=1.6587 (ny>nz=nx). It showed positive birefringence. This film had anin-plane retardation (Re) of 149 nm.

The film A-1 produced in Example 17 and the film B-4 produced above werelaminated to each other so that the fast-axes thereof were perpendicularto each other (angle, 90°). The laminated film had a thickness of 161 μmand an in-plane retardation (Re) of 134 nm. The ratio of the retardationas measured at a wavelength of 450 nm (R450) to the retardation asmeasured at a wavelength of 550 nm (R550), i.e., the ratio R450/R550,was 0.94. Furthermore, the ratio of the retardation as measured at awavelength of 650 nm (R650) to the retardation as measured at awavelength of 550 nm (R550), i.e., the ratio R650/R550, was 1.03.

Those results show that the obtained film had controlledwavelength-dispersion characteristics and reverse wavelength-dispersioncharacteristics and that it was hence suitable for use as a retardationfilm. It was suitable also as a retardation film having aquarter-wavelength retardation, i.e., as a so-called quarter-wave plate.

Example 21

The film obtained in Film Production Example 3 was cut into a squarehaving a side length of 50 mm. This cut piece was stretched byfree-width uniaxial stretching in a stretch ratio of 1.5 with abiaxially stretching apparatus (manufactured by Imoto Seisakusho) underthe conditions of a temperature of 140° C. and a stretching speed of 10mm/min (hereinafter referred to as film A-3). The film stretched wasexamined for three-dimensional refractive indexes. From the results ofthe examination (nx=1.4671, ny=1.4702, and nz=1.4725) (nx<ny<nz), thefilm obtained was found to have a low refractive index in the stretchingaxis direction and have negative birefringence. The film had an in-planeretardation Re (Re=(ny−nx)×d) of 312 nm.

The polycarbonate film obtained in Film Production Example 4 was cutinto a square having a side length of 50 mm. This cut piece wasstretched by free-width uniaxial stretching in a stretch ratio of 1.5with a biaxially stretching apparatus (manufactured by Imoto Seisakusho)under the conditions of a temperature of 170° C. and a stretching speedof 10 mm/min (hereinafter referred to as film B-5). Thethree-dimensional refractive indexes of the film obtained were:nx=1.5827, ny=1.5842, and nz=1.5827 (ny>nz=nx). It showed positivebirefringence. This film had an in-plane retardation (Re) of 130 mm.

The film A-3 and film B-5 produced above were laminated to each other sothat the fast-axes thereof were perpendicular to each other (angle,90°). The laminated film had a thickness of 177 μm and an in-planeretardation (Re) of 183 nm. The ratio of the retardation as measured ata wavelength of 450 nm (R450) to the retardation as measured at awavelength of 550 nm (R550),i.e., the ratio R450/R550, was 0.96.Furthermore, the ratio of the retardation as measured at a wavelength of650 nm (R650) to the retardation as measured at a wavelength of 550 nm(R550), i.e., the ratio R650/R550, was 1.06.

Those results show that the obtained film had controlledwavelength-dispersion characteristics and reverse wavelength-dispersioncharacteristics and that it was hence suitable for use as a retardationfilm. It was suitable also as a retardation film having aquarter-wavelength retardation, i.e., as a so-called quarter-wave plate.

Example 22

The film A-3 and film B-5 produced in Example 21 were laminated to eachother so that the angle formed by the fast-axes thereof was 80°. Thelaminated film had an in-plane retardation (Re) of 181 nm. The ratio ofthe retardation as measured at a wavelength of 450 nm (R450) to theretardation as measured at a wavelength of 550 nm (R550), i.e., theratio R450/R550, was 0.97. Furthermore, the ratio of the retardation asmeasured at a wavelength of 650 nm (R650) to the retardation as measuredat a wavelength of 550 nm (R550), i.e., the ratio R650/R550, was 1.03.

Those results show that the obtained film had controlledwavelength-dispersion characteristics and reverse wavelength-dispersioncharacteristics and that it was hence suitable for use as a retardationfilm. It was suitable also as a retardation film having aquarter-wavelength retardation, i.e., as a so-called quarter-wave plate.

Example 23

The film A-3 and film B-5 produced in Example 21 were laminated to eachother so that the angle formed by the fast-axes thereof was 70°. Thelaminated film had an in-plane retardation (Re) of 181 nm. The ratio ofthe retardation as measured at a wavelength of 450 nm (R450) to theretardation as measured at a wavelength of 550 nm (R550), i.e., theratio R450/R550, was 0.98. Furthermore, the ratio of the retardation asmeasured at a wavelength of 650 nm (R650) to the retardation as measuredat a wavelength of 550 nm (R550), i.e., the ratio R650/R550, was 1.02.

Those results show that the obtained film had controlledwavelength-dispersion characteristics and reverse wavelength-dispersioncharacteristics and that it was hence suitable for use as a retardationfilm. It was suitable also as a retardation film having aquarter-wavelength retardation, i.e., as a so-called quarter-wave plate.

Comparative Example 7

The film B-1 produced in Example 15 had an in-plane retardation (Re) of130 nm. The ratio of the retardation as measured at a wavelength of 450nm (R450) to the retardation as measured at a wavelength of 550 nm(R550), i.e., the ratio R450/R550, was 1.08. Furthermore, the ratio ofthe retardation as measured at a wavelength of 650 nm (R650) to theretardation as measured at a wavelength of 550 nm (R550), i.e., theratio R650/R550, was 0.96.

The film was poor in reverse wavelength-dispersion characteristicsbecause of the nonuse of film (A).

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the scope thereof.

This application is based on Japanese patent application No. 2006-239767filed on Sep. 5, 2006, Japanese patent application No. 2006-273046 filedon Oct. 4, 2006, Japanese patent application No. 2006-316322 filed onNov. 22, 2006, Japanese patent application No. 2007-195756 filed on Jul.27, 2007, the entire contents thereof being hereby incorporated byreference.

1. An optical compensation film or optical compensation layer, which is a film or layer comprising a fumaric ester resin, wherein the film or layer has three-dimensional refractive indexes satisfying the relationship nz>ny≧nx, wherein nx is the refractive index in a fast-axis direction of the film plane or layer plane, ny is the refractive index in an in-plane direction perpendicular to the fast-axis direction, and nz is the refractive index in an out-of-plane vertical direction, wherein the ratio of the retardation as measured at a wavelength of 450 nm to the retardation as measured at a wavelength of 550 nm (R450/R550) is 1.1 or lower.
 2. The optical compensation film or optical compensation layer according to claim 1, wherein the film or layer has an out-of-plane retardation (Rth) represented by the following expression (1), wherein d is the thickness of the film or layer, of from −30 to −2,000 nm. Rth=[(nx+ny)/2−nz]×d  (1)
 3. An optical compensation film which comprises the optical compensation film or optical compensation layer of claim 1 (film (A)) and a film (B) which has three-dimensional refractive indexes satisfying the relationship ny>nx≧nz, wherein nx is the refractive index in a fast-axis direction of the film plane, ny is the refractive index in an in-plane direction perpendicular to the fast-axis direction, and nz is the refractive index in an out-of-plane vertical direction, wherein the film (B) has an in-plane retardation (Re) as measured at a wavelength of 550 nm and represented by the following expression (2), wherein d is the thickness of the film, of 50 nm or larger. Re=(ny−nx)×d  (2)
 4. The optical compensation film according to claim 3, which has an orientation parameter (Nz) represented by the following expression (3) in the range of −0.1 to 0.95. Nz=(ny−nz)/(ny−nx)  (3)
 5. The optical compensation film according to claim 3 or 4, wherein the in-plane retardation (Re) represented by expression (2) is 50-1,000 nm.
 6. A process for producing the optical compensation film according to claim 3 or 4, which comprises laminating an unstretched film comprising a fumaric ester resin to a film obtained by uniaxially stretching a film having a positive birefringence.
 7. A process for producing the optical compensation film according to claim 3 or 4, which comprises applying a fumaric ester resin to a film obtained by uniaxially stretching a film having a positive birefringence.
 8. The optical compensation film or optical compensation layer according to claim 1 or 2, which is for use in a liquid-crystal display element.
 9. The optical compensation film according to claim 3 or 4, which is for use in a liquid-crystal display element.
 10. A retardation film which is a film comprising a fumaric ester resin and wherein when the refractive index in a fast-axis direction of the film plane, the refractive index in an in-plane direction perpendicular to the fast-axis direction, and the refractive index in an out-of-plane vertical direction are expressed by nx, ny, and nz, respectively, the refractive indexes satisfy the relationship nx<ny≦nz.
 11. The retardation film according to claim 10, which has an in-plane retardation (Re) as measured at a wavelength of 550 nm and represented by the expression (2) given above of 50-2,000 nm.
 12. The retardation film according to claim 10 or 11, wherein the ratio of the retardation as measured at a wavelength of 450 nm (R450) to the retardation as measured at a wavelength of 550 nm (R550), i.e., the ratio R450/R550, is 1.1 or lower.
 13. A retardation film comprising: a film (C) which is a film comprising a fumaric ester resin and wherein when the refractive index in a fast-axis direction of the film plane, the refractive index in an in-plane direction perpendicular to the fast-axis direction, and the refractive index in an out-of-plane vertical direction are expressed by nx, ny, and nz, respectively, the refractive indexes satisfy the relationship nx<ny≦nz; and a film (D) which has three-dimensional refractive indexes satisfying the relationship ny>nx≧nz or ny>nz≧nx, wherein nx is the refractive index in a fast-axis direction of the film plane, ny is the refractive index in an in-plane direction perpendicular to the fast-axis direction, and nz is the refractive index in an out-of-plane vertical direction.
 14. The retardation film according to claim 13, wherein the film (D) has an in-plane retardation (Re) as measured at a wavelength of 550 nm and represented by expression (2) given above of 50-2,000 nm.
 15. The retardation film according to claim 13 or 14, wherein the film (C) has an in-plane retardation (Re) as measured at a wavelength of 550 nm and represented by expression (2) given above of 50-2,000 μm.
 16. The retardation film according to claim 13, wherein the fast-axis of the film (C) forms an angle of 90°±20° with the fast-axis of the film (D).
 17. The retardation film according to claim 13 or 16, wherein the difference between the in-plane retardation (Re) of the film (C) and the in-plane retardation (Re) of the film (D) both measured at a wavelength of 550 nm is 100-160 nm.
 18. The retardation film according to claim 13 or 16, wherein the difference between the in-plane retardation (Re) of the film (C) and the in-plane retardation (Re) of the film (D) both measured at a wavelength of 550 nm is 250-300 nm.
 19. The retardation film according to claim 13, wherein the ratio of the retardation as measured at a wavelength of 450 nm (R450) to the retardation as measured at a wavelength of 550 nm (R550), i.e., the ratio R450/R550, is 1.0 or lower.
 20. The retardation film according to claim 13 or 19, wherein the ratio of the retardation as measured at a wavelength of 650 nm (R50) to the retardation as measured at a wavelength of 550 μm (R550), i.e., the ratio R650/R550, is 1.0 or higher.
 21. A composite polarizer which comprises a polarizer and the retardation film of any one of claims 10, 11, 13, 14, 16, and 19 laminated to the polarizer.
 22. A composite polarizer which comprises a polarizer and the retardation film of claim 12 laminated to the polarizer.
 23. A composite polarizer which comprises a polarizer and the retardation film of claim 15 laminated to the polarizer.
 24. A composite polarizer which comprises a polarizer and the retardation film of claim 17 laminated to the polarizer.
 25. A composite polarizer which comprises a polarizer and the retardation film of claim 18 laminated to the polarizer.
 26. A composite polarizer which comprises a polarizer and the retardation film of claim 20 laminated to the polarizer. 